This randomized double-masked clinical trial is designed to determine the value of donor selection based on histocompatibility (HLA antigen cross-match) for keratoplasty in high-risk cases. Keratoplasty recipients with dense corneal vascularization and detectable lymphocytotoxic antibodies will be randomized into two groups. One group will receive corneas from a positively cross-matched donor (lymphocytotoxic antibodies of recipients specific for one or more antigens of the donor), and the other group will receive corneas from a negatively cross-matched donor (antibodies of the recipient not specific for antigens of the donor). Corneal graft outcome will be carefully followed to determine the long term effect of recipient preimmunization. If this controlled study demonstrates that cross-match testing for donor selection has a favorable influence on the outcome of keratoplasty in recipients with densely vascularized corneas then cross-match testing should be routinely performed on such cases. Since these procedures are expensive and time consuming, antibody and cross-match testing should not be adopted as routine until they have been scientifically proven to be of value.